1. Field of the Invention
This invention relates to pushbutton key switch assemblies and more particularly to such assemblies using multi-spring actuators for each switch position.
2. Discussion of the Prior Art
Low cost, highly reliable key switch assemblies are required for many applications such as push button telephone keyboards and calculator keyboards. While many improvements have been made in key switch assemblies in recent years, such assemblies represent a significant cost or failure factor in many high volume products and further improvements are of great importance.
It is known to provide batch fabricated contact sets and switch actuators with independent spring biasing of key actuation and switch closure forces. However, the extreme precision, low cost and high reliability provided by switch contact assemblies in accordance with the present invention is not previously known.
For example, a single spring actuator arrangement is taught in U.S. Pat. No. 3,783,205 to Boulanger. The single spring of course fails to provide independent control over key actuation and contact closure forces, or precise control over the key position for switch closure notwithstanding normal tolerances in switch components. U.S. Pat. No. 3,780,237 to Seeger, Jr. et al, U.S. Pat. No. 3,856,998 to Sims, Jr. and U.S. Pat No. 3,993,884 to Kondur et al all teach dual spring key actuator arrangements. However, these arrangements do not provide the combination of precision, repeatability, and switch closure security that is attainable with a switch assembly in accordance with the present invention. For instance, only the patent to kondur et al teaches positioning of the follower, but assembly is quite complex with many latches, catches and washers and cannot be accomplished from a single side. None of these references teach the advantages of combining a dual spring actuator with a third spring comprised of a truncated cone contact or the contact configuration of this invention.
Disclosure of switch contact assemblies can be found in U.S. Pat. Nos. 3,383,487 to Weiner, 3,699,294 to Sudduth and 3,860,771 to Lynn et al. However, the combination of simplicity, cone spring switch contact assembly, high security circuit pattern and excellent actuator assembly taught by this application are not disclosed.